Noun
English Wikipedia has an article on:dark nebulaWikipedia
dark nebula (plural dark nebulas or dark nebulae)
(astronomy) A type of nebula that does not emit or reflect (visible) light, and thus obscures light sources behind it.
Synonym: dark cloud
The Horsehead Nebula is a typical dark nebula, and is famous for resembling the head of a horse.
Deep-sky objects The Coalsack Nebula is the most prominent dark nebula in the skies, easily visible to the naked eye as a prominent dark patch in the southern Milky Way. Source: Internet
The black patch of sky is a vast hole of empty space and not a dark nebula as previously thought. Source: Internet